Ethanol for industrial use is conventionally produced from organic feed stocks, such as petroleum oil, natural gas, or coal, from feed stock intermediates, such as syngas, or from starchy materials or cellulose materials, such as corn or sugar cane. Conventional methods for producing ethanol from organic feed stocks, as well as from cellulose materials, include the acid-catalyzed hydration of ethylene, methanol homologation, direct alcohol synthesis, and Fischer-Tropsch synthesis. Hydration of ethylene is described in U.S. Pat. Nos. 3,686,334; 3,953,533; 4,003,952; 4,329,520; 4,351,970; 4,956,506; 5,349,096; 5,684,216; and 6,072,090. Instability in organic feed stock prices contributes to fluctuations in the cost of conventionally produced ethanol, making the need for alternative sources of ethanol production all the greater when feed stock prices rise. Starchy materials, as well as cellulose materials, are converted to ethanol by fermentation. However, fermentation is typically used for consumer production of ethanol, which is suitable for fuels or human consumption. In addition, fermentation of starchy or cellulose materials competes with food sources and places restraints on the amount of ethanol that can be produced for industrial use.
Ethanol production via the reduction of alkanoic acids and/or other carbonyl group-containing compounds has been widely studied, and a variety of combinations of catalysts, supports, and operating conditions have been mentioned in the literature. During the reduction of alkanoic acid, e.g., acetic acid, other compounds are formed with ethanol or are formed in side reactions. These impurities limit the production and recovery of ethanol from such reaction mixtures. For example, during hydrogenation, esters are produced that together with ethanol and/or water form azeotropes, which are difficult to separate. In addition when conversion is incomplete, unreacted acid remains in the crude ethanol stream, which must be removed to recover ethanol.
EP02060553 describes a process for converting hydrocarbons to ethanol involving converting the hydrocarbons to ethanoic acid and hydrogenating the ethanoic acid to ethanol. The stream from the hydrogenation reactor is separated to obtain an ethanol product and a stream of acetic acid and ethyl acetate, which is recycled to the hydrogenation reactor.
In addition impurities, water is co-produced with ethanol during hydrogenation and distillation of ethanol and water is difficult to obtain anhydrous ethanol that is more suitable for fuel applications. Membranes have been proposed to remove water, such as those described in U.S. Pub. No. 2008/0207959 and U.S. Pat. Nos. 7,732,173; 7,594,981; and 4,774,365.
The need remains for improved processes for efficiently producing ethanol and reducing water content.